The present invention relates to an active matrix display screen without intersection of the addressing row and column collectors. It is used in optoelectronics in the production of liquid crystal displays more particularly used as converters of electrical information into optical information.
Most liquid crystal display screens with a complexity equal to or greater than 10.sup.5 elementary image points use a matrix addressing mode. This addressing mode has limitations, which are in particular studied in the article "Perspective actuelle de presentation de'mages sur panneaux plats" which appeared in the Journal "OPTO", No. 6, September 1981, pp. 29 to 31. These limitations mainly relate to the addressing selectivity of an elementary image point and to the displaying speed.
In order to select a particular image point, it is necessary for the potential difference between the row and the column at the intersection of which the image point is located to exceed a threshold voltage V.sub.s and simultaneously the voltage at each of the other image points is significantly below the threshold voltage V.sub.s. This is generally realised by applying carefully chosen non-zero voltages to the unselected rows and columns. This leads to high energy costs, which increases in linear manner with the number of rows.
Moreover, the higher the number of displaying rows, the higher the writing speed. Thus, there is only a small time interval between the writing of two successive rows and the necessary average power increases. Consequently, there is a compromise between the screen size, the available power and the addressing speed.
In order to exceed the limits of matrix addressing, a known solution consists of incorporating the electrical threshold and the memory effect at each image point. This threshold can be ensured by a thin film transistor, a varistor or by a MIM (metal-insulator-metal) switch or the like. Such a structure is said to be an active matrix structure. In such an active matrix, each image point is located at the intersection of a connecting column and row and is constituted e.g. by a transistor and a capacitor.
In the case where the optoelectronic transducer is a liquid crystal, the coatings or armatures of the capacitor can be constituted by the electrodes of the actual liquid crystal cell. The image point consequently amounts to a transistor and a capacitor, whereof one of the coatings is constituted by the electrode placed on the wall of the cell containing the transistor and the other coating is constituted by the opposite electrode placed on the other cell wall.
Such a structure is shown in FIG. 1. It is possible to see on the one hand a lower wall 10 carrying the conducting columns 12 and conducting rows 14, a thin film transistor 20 and a transparent electrode 22, and on the other hand an upper wall 24 covered with an also transparent opposite electrode 26.
At each intersection 28 between the conductor rows and columns, it is obviously necessary to ensure the electrical insulation between the conductors. This is one of the problems which has not been satisfactorily solved up to now. Thus, there are numerous short-circuits at these intersections, so that frequently the active matrix cannot be used and consequently there is a significant drop of output.
To obviate these disadvantages, the invention proposes an active matrix structure eliminating these intersections of row and column conductors.